1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a heat dissipation system for a semiconductor device, having an improved heat dissipation structure to control noise.
2. Description of the Related Art
Due to the development of a semiconductor technology, a semiconductor electric energy is widely used as, for example, a converted thermal energy, mechanic energy, electric energy or the like by a power device. An active switching device used in semiconductor power devices, such as a BJT (Bipolar Junction Transistor), a FET (Field Effect Transistor) and an IGBT (Insulated Gate Bipolar Transistor), can be on/off according to a user's signal. Recently, an intelligent power module (IPM), or an active power device further including a control chip to control a power device has been developed.
In a switching operation, a self-temperature of a power device is increased by a conduction loss generated due to a parasitic resistor on operation of a switching device and by a switching loss generated due to a switching operation (continual on/off operation). Generally, in order to dissipate heat generated from the conduction loss and the switching loss, a metal plate is attached to one side of the power device to dissipate the heat.
FIG. 5 shows a conventional power converting system including an IPM 10, which is used as a power device, and a control board 50. A metallic base plate 11 is provided in a base side of the power device 10 so as to increase the heat dissipation property. An insulating layer 13 is formed on the base plate 11. A predetermined circuit pattern (not shown) is provided on the insulating layer 13. A plurality of semiconductor chips 14 and 15 are provided according to the predetermined circuit pattern provided on the insulting layer 13. The semiconductor chips 14 and 15 are bonded to one another by wires and are included in the power device.
FIG. 6 shows an inverter circuit comprising a plurality of switching devices 14a, which corresponds to FIG. 5. Each of the switching devices 14a includes an active power device, for example, an IGBT. The inverter circuit further includes a pattern of a control chip 15a which performs a PWM (Pulse Width Modulation) control over a switching operation of the switching devices 14a according to a gate signal. That is, the control chip 15a performs the PWM control and supplies power, which is converted to an intended frequency and voltage by on/off operation of each switching device 14a, to a load (i.e., a motor). The control chip 15 also transmits all kinds of information on the IPM 10 to a control board 50. The information on the IPM 10 includes over current, short-circuit current and overheat information of each switching device 14a, and over voltage and under voltage information of a controlled source. To increase the heat dissipation property of the power device 10, an exterior heat sink 40 is adhered closely to the base plate 11 of the power device 10 by a glue (not shown) and/or screws 12.
Although the base plate 11 of the power device 10 and the exterior heat sink 40 are laid out to be flat, to engage with each other, a predetermined gap is formed therebetween by a manufacturing tolerance, thereby decreasing the heat dissipation efficiency. Thus, an insulating material 30, such as grease, having a high thermal conductivity is filled into the gap formed between the base plate 11 and the exterior heat sink 40. However, the non-conductive grease works as a dielectric, so as to generate a parasitic capacitance 31 between the base plate 11 and the exterior heat sink 40.
Because an interior of the semiconductor power device 10 is laid out to have high insulating resistance, an outside voltage (in the case of a diode) or a gate signal (in the case of an active device) has to be applied so as to perform a switching operation by an on/off operation of the switching devices 14a. However, where noise from a power source, lightning, or other external high voltage is applied to the power device 10, an insulating resistor in the interior of the power device 10 can be broken down, or the switching devices 14a can be operated by a signal distortion, to thereby induce the break down of the power device 10 and a system using the same.
As described above, FIG. 6 illustrates an interior circuit of the IPM 10 and the control board 50 of a power converting system of FIG. 5, and illustrates that three-phase AC power is converted to DC power and the converted DC power is supplied to a three-phase AC servo motor through an inverter. That is, exterior three-phase AC power is supplied from an AC power terminal 60 through an electric wire 61 and is converted to DC power through a rectifying circuit 51 and 52 provided in the control board 50. The converted DC power passes through an inverter circuit including six switching devices 14a of the IPM 10 and is supplied to a terminal 70 of a AC servo motor in a side of the load connected to an output line 71, to thereby drive the motor. An SMPS (Switching Mode Power Supply) 53 and a control circuit 54 provided in the control board 50 control an actuation of the control chip 15a to control the switching devices 14a. 
Generally, a ground contact part 41 of the exterior heat sink 40 is connected to a ground line 42 in a side of the power supply and an ground line 43 in a side of the load by screws. Y-capacitor 55 is connected between each electric wire 61 and the ground line 42.
In the above circuit, where a lightning, that is, noise of the power supply (high voltage spike occurring in a relay or a field) or the like, is applied to the electric wire 61 and the output line 71 connected outward, common mode noise occurs. Energy generated by the common mode noise is laid out to pass through the Y-capacitor 55 and to flow off through the grounded exterior heat sink 40 toward the ground line 42 in the side of the power supply, to thereby protect the internal circuit of the power device 10. At this point, capacitance of the Y-capacitors 55 can be increased to increase the tolerance against the noise. However, in this case, the amount of a leakage current is increased. Where the noise-like energy, which does not flow off through the Y capacitors 55, is charged to an internal parasitic capacitance (generated between each switching device 14a and an interior heat dissipation member (not shown)) of the power device 10 and the external parasitic capacitance 31, the switching devices 14a are operated by the lowest electric potential, to thereby enable an erroneous operation of the circuit to be induced. That is, in a switching operation of the power device 10, where two switching devices 14a in an upper and a lower sides of the inverter circuit of FIG. 6 are simultaneously turned on, and thus induce a short circuit of a DC link, the circuit can be broken down.
In the case that the common mode noise occurs, the energy induced by the noise is stored in the parasitic capacitance created in the semiconductor power device, and thus exerts negative effects such as the erroneous operation of the system and/or the circuit breakdown.